I have a netbook with no CD drive. I wanted to upgrade its OS from 10.04 to 12.04. I downloaded to it the alternate iso, mounted that and ran the upgrade from it, all in accordance with instructions...

I'm using Ubuntu 10.04 on two computers, my current one and my old one. I want to upgrade to 12.04. I thought I'd try to upgrade on my old computer first, just to familiarise myself with the process...